Paget’s disease A chronic bone disorder that typically results in enlarged, deformed bones due to excessive breakdown and formation of bone tissue that can cause bones to weaken and may result in bone pain, arthritis, bony deformities, and fractures. Paget’s disease generally occurs in persons over the age of 40 years. Men and women are…
pachyonychia congenita An inherited condition that is characterized by abnormally thick, curved nails; thickening of the skin of the palms, soles, knees, and elbows; and white plaques in the mouth. Abbreviated PC. There are two distinct syndromes of PC. The basic abnormality in both is a mutation in one of the genes for keratin, which…
pacemaker, natural See sinoatrial node.
pacemaker, implantable A pacemaker in which the electrodes to the heart, the electronic circuitry, and the power supply are all implanted internally within the body.
pacemaker, artificial An electronic device that uses electrical impulses to regulate the heart rhythm. A pacemaker may be external (located outside the body) or internal (implanted in the body). Although there are many different types of pacemakers, all are designed to treat bradycardia, a tooslow heart rate. Pacemakers may function continuously and stimulate the heart…
pacemaker A device or system that sends electrical impulses to the heart in order to set the heart rhythm. A pacemaker can be the natural pacemaker of the heart (the sinoatrial node) or it can be an electronic device that serves as an artificial pacemaker. See also pacemaker, artificial; pacemaker, implantable; sinoatrial node.
PA X-ray An X-ray picture in which the beams pass from back to front (posteroanterior), as opposed to an AP (anteroposterior) film, in which the rays pass through the body from front to back.
p arm of a chromosome The short arm of a chromosome. Each human chromosome has two arms—a short arm and a long arm. By international convention, the short arm is termed p, and the long arm is termed q. For example, if a gene is on 4p12, that gene is on the short arm of…
p 1 In biochemistry, protein. For example, p53 is a protein that has a mass of 53 kilodaltons. 2 In population genetics, the frequency of the more common of two different alternative (allelic) versions of a gene. (The frequency of the less common allele is q.) 3 In statistics, probability.
oz. Abbreviation for ounce.
oz. oxyuris A group of intestinal worms that includes pinworm.
oxytocin A hormone made in the brain that plays a role in childbirth and lactation by causing muscles to contract in the uterus and in the mammary glands. Oxytocin is secreted by the hypothalamus and transported to the posterior lobe of the pituitary gland at the base of the brain. See also pituitary, posterior.